Fix Courseware's image upload.

Closes #350.

lib/classes/JsonApi/Routes/Courseware/StructuralElementsImageDelete.php

@@ -11,7 +11,7 @@ use Psr\Http\Message\ServerRequestInterface as Request;
 
 class StructuralElementsImageDelete extends NonJsonApiController
 {
-    public function invoke(Request $request, Response $response, array $args)
+    public function invoke(Request $request, Response $response, array $args): Response
     {
         if (!($structuralElement = StructuralElement::find($args['id']))) {
             throw new RecordNotFoundException();

lib/classes/JsonApi/Routes/Courseware/StructuralElementsImageUpload.php

@@ -17,7 +17,7 @@ class StructuralElementsImageUpload extends NonJsonApiController
 {
     use CoursewareInstancesHelper, FilesRoutesHelper;
 
-    public function invoke(Request $request, Response $response, array $args)
+    public function invoke(Request $request, Response $response, array $args): Response
     {
         if (!($structuralElement = StructuralElement::find($args['id']))) {
             throw new RecordNotFoundException();

lib/classes/JsonApi/Routes/Files/FileRefsContentShow.php

@@ -14,7 +14,7 @@ class FileRefsContentShow extends NonJsonApiController
 {
     use EtagHelperTrait;
 
-    public function invoke(Request $request, Response $response, array $args)
+    public function invoke(Request $request, Response $response, array $args): Response
     {
         if (!$fileRef = \FileRef::find($args['id'])) {
             throw new RecordNotFoundException();

lib/classes/JsonApi/Routes/Files/FileRefsContentUpdate.php

@@ -13,7 +13,7 @@ class FileRefsContentUpdate extends NonJsonApiController
 {
     use RoutesHelperTrait;
 
-    public function invoke(Request $request, Response $response, array $args)
+    public function invoke(Request $request, Response $response, array $args): Response
     {
         if (!$fileRef = \FileRef::find($args['id'])) {
             throw new RecordNotFoundException();